hi, i develop here on indeXus.Net Shared Cache which is something similar to Cache Application block. So I do not use application
block at all so far and can't give you good advise about it since I do not have any experience with it, sorry. regards, roni

We are using CAB and ASP caching at the same time. If you ask me, I would use CAB.
ASP.Net Caching Pros:
- Fast (Yes, it performs better)
- More proven than CAB.
- Built in to the system, every developer has it.

CAB Pros:
- Multi platform. Works on Web or Windows or any other context. No dependency on HTTP Context.
- Provides multi backing stores (Database, File, memory or on your own -eg. you can cache on Exchange server if you want :P )
- Source available
- Better extensibility and software design (which costs performance)
- Integrity to Instrumentation and WMI with performance counters
- Multiple caching stores

If you are building Web applications "only" then use ASP.Net caching. But if you write nightly tasks (tiny EXEs) that also uses the same caching architecture, I recommend CAB.
Also as you can see CAB has more features but slower. Do you need those features or source code?
My vote goes to CAB. These are my opinions.